Steven Sinofsky, who stepped down as head of Microsoft’s Windows business last fall, is joining the cloud storage startup Box as an adviser.

Box CEO Aaron Levie announced the move in a blog post Thursday, saying the pairing started with a Facebook message.

I’ve gotten to know Steven over the past six months. It all started with an unsolicited Facebook message last fall, and not only did Steven not block me, he graciously responded. In fact, he even visited Box HQ to learn about what we are working on.

Steven has a stronger and more fluid vision for the future of computing than almost anyone I’ve met. As we kept talking and sometimes meeting over Pho, I realized we had to get him involved with Box.

In his more than 20 years at Microsoft, Sinofsky worked on some of the company’s biggest products, including Windows and Office. He was also involved with the online-storage service SkyDrive, which competes in a growing space that includes Box, DropBox and Google Drive.

Sinofsky now brings that document-management experience to Box, which focuses on the workplace.“I’m excited to work Aaron and team to lend my experience to furthering the Box vision of the enterprise,” Sinofsky said.

On his Twitter account, Sinofsky poked fun at his manifesto-length written insights: